Angioplasty is used to increase the lumen diameter of an artery where the artery has become narrowed, or stenosed, for a variety of reasons. Balloon angioplasty has been successfully used in the placement of stents to permanently enlarge such a stenosis, especially in coronary arteries. Numerous coronary stents have been provided in the prior art that are adapted to provide a uniform expansion of the stent in a lumen wall. One example of a type of prior art include stents formed of wire wound around a mandrel. Another type of prior art includes stents formed of thin-walled metal tubes cut to permit compression for delivery . These prior art tubular stents have limited longitudinal stability when expanded. Both of these types of prior art stents require a preliminary step to expand the diameter of the lumen to be stented. These stents also, when implanted, expand to a uniform diameter without regard to the twists and turns of the lumen wall.
While these stents may be suitable for the particular purpose to which they address, they would not be as suitable for the purposes of the present invention as hereafter described. Therefore, a need exists for a stent that provides longitudinal flexibility in combination with increased hoop strength, torsional stability, longitudinal stability and radial flexibility. The stent of the present invention provides these attributes by being formed of a relatively high percentage of metal material providing a high hoop strength to the stent while the stent wall surface pattern delivers a high degree of flexibility while permitting a small amount of longitudinal foreshortening. The stent of the present invention can be applied in a one-step process eliminating the need for a preliminary step dilating the lumen into which the stent is to be placed. It should be noted that the invention is not limited to the applications mentioned which must be considered as solely exemplifying.
It is an object of the present invention to provide a stent for use in human blood vessels, primarily coronary arteries.
It is a further object of the present invention to provide a stent having the flexibility to present a small cross-section for ease of positioning for implantation while being radially expandable for implantation with a relatively high xe2x80x9choopxe2x80x9d strength as a result of a relatively high percent metal stent surface providing a relatively large metal surface area to free space ratio.
It is an object of the present invention to provide a radially expandible stent with a unique stent wall surface pattern.
I it is an object of the present invention to provide a stent having a relatively small diameter eliminating the need for the preliminary step of expanding the lumen into which the stent is to be placed.
It is a further object of the present invention to provide a stent with minimal longitudinal foreshortening upon expansion in situ.
It is a further object of the present invention to provide a stent with the flexibility to be placed in a curved, narrow lumen in combination with the ability to be expanded in a non-uniform manner to fit the particular lumen size and shape.
The present invention is directed to a stent that satisfies these needs to provide both flexibility and strength in a radially expandable stent. Both are provided as a result of a relatively large metallic surface area, compared to free space, and because of the unique stent wall surface pattern. The un-expended stent has a small cross-section, for case of implantation with balloon angioplasty, and yet offers, increased hoop strength when expanded at the time it is implanted or embedded into the lumen wall. In the un-expanded form immediately after laser cutting, the surface wall pattern resembles a series of continuous S-shapes formed radially about the tube with interconnections between the radial rows of S""s with alternating adjacent S""s. Longitudinally, the un-expanded stent resembles longitudinal rows of pattern series of an S, S, reverse S, reverse S shapes. This series repeats itself along the longitudinal surface of the stent. The longitudinal pattern is interconnected by the radial S""s. In the expanded form, the stent wall surface pattern resembles a connected line of parallelograms along its longitudinal axis while interconnected radially to diamond shapes with alternating connected and disjointed struts form a pattern similar to a butterfly shape, along its radial axis. Because the stent of the present invention is so flexible, the stent can be used in a variety of vessel sizes for repair of fistula, lesions, stenosises, and aneurism . Because a relatively high percentage of metal is used in the present invention, as compared to prior stents, the pattern of the stent delivers a very high hoop strength that is required to prevent re-stenosis. It is planned that the stent will not routinely be expanded to its maximum size. This enables the stent to be formed to fit the lumen into which it is implanted, be it twisted, curved or the like. The expanded outside edges of the stent are, upon expansion of the stent, received into the lumen wall preventing formation of blood clots at the site of the stent.
Another aspect of the stent provides an alternative embodiment with a multi-layer stent that further increases the metal surface area increasing the radial hoop strength of the stent without sacrificing flexibility.
Another aspect of the stent provides a method of implantation of the stent wherein the stent is crimped onto the balloon for balloon angioplasty placement without the preliminary lumen expansion step.
Another aspect of the stent of the present invention also provides a method of manufacturing such a stent.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.